This invention relate to a power supply apparatus for arc-utilizing apparatuses, such as DC arc welders, DC arc cutters and discharge lamp ignition devices, and, more particularly, to such apparatus that can operate from any one of plural different-valued AC voltage sources.
A power supply apparatus for an arc-utilizing apparatus sometimes needs to be used with either a high-voltage commercial AC power supply supplying a voltage of the order of, for example, 400 V or a low-voltage commercial AC power supply supplying a voltage of the order of, for example, 200 V.
There are plurality of low-voltage commercial AC power supplies, which provide an output voltage of, for example, 200 V, 208 V, 230 V and 240 V. Also, there are plural high-voltage commercial AC power supplies, which provide an output voltage of, for example, 380 V, 400 V, 415 V, 440 V and 460 V. Regions where high-voltage commercial AC power supplies are used and regions where lower-voltage commercial AC power supplies are used mingle in some area. In such area, a user must be very careful to determine an appropriate power supply apparatus.
Power supply apparatus manufacturers, too, must manufacture both high-voltage power supply apparatuses and low-voltage power supply apparatuses and store them. Sales agencies, too, must stock power supply apparatuses of both types. This is a burden on both manufacturers and sales agencies in view of manufacturing cost and stocking space.
A power supply apparatus which can operate from either of high-voltage and low-voltage power supplies has been long desired. One example of such power supply apparatuses is disclosed in Japanese (Unexamined) Patent Application Publication No. HEI 11-77302 (A) laid open for public inspection on Mar. 23, 1999. A circuit similar to this prior art apparatus is shown in FIG. 1. A commercial AC supply voltage applied to input supply terminals 1a, 1b and 1c is coupled through a switch device 2 to an input-side rectifier 4 for rectification. The rectified voltage from the input-side rectifier 4 is raised in a voltage-boosting converter 8, which includes a reactor 10, an IGBT 12, a current detector 14 and a reverse-current blocking diode 16. The boosted voltage is developed between output terminals P and N of the voltage-boosting converter 8.
A switching unit 18 which may include a normally-open switch 20a, a normally-closed switch 20b and a normally-open switch 20c, is connected between the output terminals P and N. By properly opening and closing these switches 20a-20c, smoothing capacitors 22 and 24 are connected in series or in parallel between the output terminals P and N.
Inverters 30 and 40 are connected across the smoothing capacitors 22 and 24, respectively. The inverter 30 is a half-bridge type inverter formed of IGBTs 32a and 32b, capacitors 34a and 34b, and flywheel diodes 36a and 36b. Similarly, the inverter 40 is a half-bridge type inverter formed of IGBTs 42a and 42b, capacitors 44a and 44b, and flywheel diodes 46a and 46b. The inverters 30 and 40 develop high-frequency voltages as their output voltages, which are applied to voltage-transformers 50 and 52, respectively.
The transformed voltages are applied to output-side rectifiers 54 and 56, respectively, formed of diodes 54a and 54b and diodes 56a and 56b, respectively, where they are rectified. The rectified voltages are combined and smoothed in a smoothing reactor 58 before appearing between output terminals 60P and 60N of the power supply apparatus. The voltage developed between the output terminals 60P and 60N is applied to a load.
A current flowing through the load is detected by a current detector (CD) 62, and a controller 64 controls the conduction periods of the IGBTs 32a, 32b, 42a and 42b in accordance with a current-representative signal representing the detected load current, to thereby maintain the load current constant.
A switching control unit 66 controls the switching unit 18. The switching control unit 66 detects the voltage between the input terminals 1a and 1b and opens the normally-open switches 20a and 20c, while closing the normally-closed switch 20b, when it detects a high-voltage commercial AC supply being connected to the input of the apparatus. This causes the capacitors 22 and 24 to be connected in series between the terminals P and N. If the power supply connected to the input of the apparatus is a low-voltage commercial AC power supply, the switching control unit 66 closes the normally-open switches 20a and 20c and opens the normally-closed switch 20b, which makes the capacitors 22 and 24 connected in parallel between the terminal P and N.
The voltage boosting converter 8 is controlled by a converter control unit 68. A reference signal source 70a to be used in association with higher commercial AC voltages is connected to the converter control unit 68 through a normally-closed switch 20e, and a reference signal source 70b to be used in association with lower commercial AC voltages is connected to the converter control unit 68 through a normally-open switch 20d. The switches 20e and 20d are also controlled by the switching control unit 66.
The voltage appearing between the output terminal P and N is detected by a voltage detector 26, which develops a voltage-representative signal representing the detected voltage. The voltage-representative signal is applied to the converter control unit 68.
When one of the high-voltage commercial AC power supplies is connected to the input terminals 1a-1c, the switching control unit 66 causes the normally-closed switch 20e and the normally-open switch 20d to be maintained closed and open, respectively. Then, the converter control unit 68 controls the voltage-boosting converter 8 in accordance with the voltage-representative signal from the voltage detector 26 and a reference signal provided by the reference signal source 70a, in such a manner that a voltage of about 640 V, which is equal to {square root over (2)}xc3x97460 V, can be developed between the output terminals P and N. The voltage of 460 V is the highest one of the high-voltage power supply voltages. Since the normally-open switches 20a and 20c are open, while the normally-closed switch 20b is closed when the high voltage is applied to the apparatus, the capacitors 22 and 24 are connected in series, and, therefore, the voltage applied to each of the inverters 30 and 40 is about 320 V.
The converter control unit 68 controls the voltage-boosting converter 8 in accordance with the current-representative signal from the current detector 14, too, in order to improve the power factor.
When one of the low-voltage commercial AC power supplies is connected to the input terminals 1a-1c, the switching control unit 66 opens the normally-closed switch 20e and closes the normally-open switch 20d. Then, the converter control unit 68 controls the voltage-boosting converter 8, in accordance with the voltage-representative signal from the voltage detector 26 and the reference signal from the reference signal source 70b, in such a manner that a voltage of about 320 V can be developed between the output terminals P and N. Since the normally-open switches 20a and 20c are closed with the normally-closed switch 20b opened, the capacitors 22 and 24 are connected in parallel with each other, so that the voltage applied to each of the inverters 30 and 40 is about 320 V. In this case, too, the power factor is improved by the voltage-boosting converter 8.
As described above, whether a high-voltage commercial AC power supply or a low-voltage commercial AC power supply is connected to the input terminals 1a-1c, the voltage applied to each of the inverters 30 and 40 is about 320 V. Accordingly, as the IGBTs 32a, 32b, 42a and 42b of the inverters 30 and 40, general-purpose IGBTs withstanding a collector-emitter voltage of, for example, about 600 V can be used.
However, since the IGBT 12 of the voltage-boosting converter 8 may receive a voltage of as high as 640 V, an IGBT having an emitter-collector withstand voltage of 1200 V or higher must be used. Also, the single voltage-boosting converter 8 is used to supply current to the two inverters 30 and 40, a large current will flow through the IGBT 12 when it is turned on and off. Therefore, the IGBT 12 must a large capacity IGBT. Accordingly, a general-purpose IGBT as used in the inverters 30 and 40 cannot be used as the IGBT 12.
An object of the present invention is to provide a power supply apparatus with a voltage-boosting converter which uses a general-purpose semiconductor switching device.
According to the present invention, a power supply apparatus adapted for use with an arc-utilizing apparatus has input terminals adapted to be connection to one of commercial AC power supplies in first and second groups. Each of the first and second groups of commercial AC power supplies includes a plurality of power supplies providing output voltages of different magnitudes. The magnitudes of the output voltages of the first group of commercial AC power supplies are about two times as large as the output voltages of the second group commercial AC power supplies.
A rectifier rectifies a commercial AC voltage applied to the input terminals and develops a rectified voltage between two rectifier output terminals. A switching unit connects two voltage-boosting converters between the two rectifier output terminals either in series or in parallel with each other. A DC-to-high-frequency converter is connected in the output of each of the voltage-boosting converters, for converting a voltage applied to it into a high-frequency voltage.
The high-frequency voltage from each of the DC-to-high-frequency converters is applied to a primary side of a transformer. A high-frequency voltage induced in a secondary side of the transformer is converted to a DC voltage in a high-frequency-to-DC converter, and the resulting DC voltage is developed between two load output terminals.
When the commercial AC power supply connected to the input terminals is one of the first group, a switching control unit controls the switching unit so as to connect the voltage-boosting converters in series between the rectifier output terminals. If the commercial AC power supply connected to the input terminals belongs to the second group, the switching control unit controls the switching unit so as to connect the voltage-boosting converters in parallel between the rectifier output terminals.
With the above-described arrangement, regardless whether the voltage-boosting converters are connected in series or in parallel, the highest voltage applied to each voltage-boosting converter is about a half of the highest one of the voltages provided by the commercial AC power supplies of the first group. Accordingly, the semiconductor switching device of each voltage-boosting converter is required to withstand a lower voltage than prior art apparatuses.
Control means controls the two voltage-boosting converters so as to provide substantially equal DC voltages to the associated DC-to-high-frequency converters regardless whether the commercial AC power supply connected to the input terminals of the apparatus is of the first group or of the second group.
Accordingly, if the DC-to-high-frequency converters include semiconductor switching devices, it is sufficient for the semiconductor switching devices to withstand the DC voltages supplied from the associated voltage-boosting converters.
The control means may control the respective voltage-boosting converters in such a manner that they supply to the associated DC-to-high-of-frequency converters, about a half of the voltage resulting from rectifying the highest one of the voltages supplied by the commercial AC power supplies of the first group.
With the above-described arrangement, the semiconductor switching devices of the voltage-boosting converters need to withstand only the voltage of one half of the highest one of the commercial AC voltages which can be supplied by the first group of commercial AC power supplies. Thus, there is no need for using specially designed semiconductor switching devices withstand high voltages, but general-purpose ones can be used.